Process for recycling hardened polysulphide and/or polymercaptan adhesives and sealants

ABSTRACT

The invention relates to a process for recycling cured or partly cured polysulfide and/or polymercaptan compositions. Recycling is carried out in a non-volatile liquid with addition of a depolymerizing agent, preferably a sulfur-containing vulcanization accelerator known from rubber technology. The depolymerisate may be added to the curing component of two-component polysulfide and/or polymercaptan adhesives/sealants or coating materials in large quantities without any significant effect on its stability in storage or curing characteristics.

BACKGROUND OF THE INVENTION

This invention relates to a process for recycling cured or partly curedpolysulfide and/or polymercaptan polymer compositions.

One-component or multi-component compositions based on polysulfidepolymers and/or polymercaptan polymers are used in civil engineering andbuilding construction, in the aircraft or automotive industry, inshipbuilding and, on a large scale, in the manufacture of insulatedglass. Both in the case of industrial application in automobileconstruction, in shipbuilding, in aircraft construction and in themanufacture of insulated glass, the sealants, adhesives or coatingmaterials used accumulate as residual materials and waste in partly orcompletely cured form. Compositions based on polysulfide polymers and/orpolymercaptans are distinguished in particular by their high resistanceto light and ozone and by their resistance to numerous solvents andchemicals. For this reason, adhesives/sealants based on polysulfides orpolymercaptans have long been used, for example, for the production ofinsulated glass (see, for example, H. Lucke, "Aliphatische Polysulfide",Heidelberg (1992), page 114).

In the case of one-component, systems, cured or partly cured residuesare actually formed during production in the production plants; duringprocessing, residues remain in the processing machines and processingcontainers. In the case of multi-component systems, partly or completelycured residues are formed in the material-carrying parts of processingmachines, at the beginning of production or when the machines areswitched off and when they are cleaned by "rinsing" and when excessquantities are removed during application to the structural componentsor vehicles. Non-reusable, solid elastomers hitherto disposed of aswaste are also accumulating to an increasing extent at the end of theuseful life of those parts in which the elastomers were used. Sincepolysulfides and--polymercaptans have already been in use for severaldecades as adhesives for the production of laminated insulated glass andas joint sealing compounds and coating materials in civil engineeringand building construction, cured adhesives/sealants or coating materialswhich, hitherto, have had to be disposed as waste accumulate duringrebuilding, renovation and dismantling.

Accordingly, there is a need for processes which enable these materialsto be recycled.

DE-C-4142500 describes a process for recycling cured polysulfide and/orpolymercaptan elastomers. According to this document, 0.5 to 400% byweight of cured elastomer are reacted in a liquid dimercapto orpoly-mercapto compound to form liquid, paste-like mercapto-terminatedpre-polymers and the prepolymers thus obtained are reused as polysulfideand/or polymercaptan sealing compounds. Although this method basicallyprovides useful results, the stability in storage of the polysulfidecomponent produced in this way is unsatisfactory. Thus, the formation ofa thick skin of at least partly cured adhesive/sealant or coatingmaterial on the surface of the polysulfide-containing component isobserved after only a relatively brief storage period, depending on thequantity of "recyclate" introduced. It is assumed that this hardeningreaction is brought about by atmospheric oxygen in conjunction with theaminic constituents which have entered the polysulfide component throughthe recycling process.

Accordingly, there was a need to find an improved process for recyclingcured polysulfide and/or polymercaptan compositions, in which thecompositions containing the recycled products would not have anyproblems in regard to stability in storage.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, the solution to this problem ischaracterized in that the cured or partly cured polysulfide and/orpolymercaptan polymer compositions are first depolymerized by adepolymerizing agent and the depolymerisate is subsequently incorporatedin the curing component of two-component of multi-component polysulfideand/or polymercaptan compositions.

The degradation or partial degradation of polysulfide compositions bydepolymerizing agents has been known for some time. Thus, U.S. Pat. No.2,548,718 describes a composition for degrading coatings based onpolysulfide elastomers. According to this document, a reaction productof one or more dialkylamines and carbon disulfide in solvents, forexample ketones or halogenated hydrocarbons, is used to degradepolysulfide coatings. However, the degradation product is discarded aswaste and is not recycled.

EP-B-188 833 describes a process for cleaning machinery soiled withpolymer residues of rubber-like polysulfide elastomers. This processuses a mixture of an organic solvent, a chain-terminating agent orchain-degrading agent of mercaptofunctional compounds and an amine asreaction accelerator. According to the teaching of this document, thesolvent used can be recycled whereas the fate of the degraded polymerresidues is not discussed.

According to the invention, the cured or partly cured polysulfide and/orpoly- mercaptan compositions are size-reduced and depolymerized in alow-viscosity non-volatile liquid to which the depolymerizing agent isadded. Plasticizers are preferably used as the low-viscositynon-volatile liquid. In principle, any low-viscosity plasticizer may beused for this purpose, although it is preferred to use thoseplasticizers which are also used in curing pastes for two-component ormulti-component polysulfide or polymercaptan systems.

Examples of such plasticizers are alkyl sulfonic acid esters ofphenol/cresol, alkyl and/or aryl phosphates, dialkyl esters of aliphaticdicarboxylic acids and, in particular, dialkyl or aryl esters ofphthalic acid. Benzyl butyl phthalate is most particularly preferred.

In principle, any depolymerizing agent may be used. According to theinvention, the vulcanization accelerators known from rubber technology,including for example thiazole accelerators, thiurams, dithiocarbamates,dithiocarbamyl sulfenamides, xanthogenates, sulfur-containing triazineaccelerators, thiourea derivatives or other basic sulfur compounds, arepreferred. These depolymerizing agents may optionally be used incombination with other basic compounds, such as amines or guanidinecompounds. In one particularly preferred embodiment, aqueous solutionsof the salts of dithiocarbamates, xanthogenates, thiourea derivatives,thiazole derivatives or other basic sulfur compounds are used asdepolymerizing agents.

The depolymerization is carried out with stirring in a vessel attemperatures of 0 to 100° C. and preferably at an elevated temperatureof 50 to 90° C. Although generally not necessary, the depolymerizationmay even be carried out under pressure in an autoclave so that thetemperatures may even be above 100° C. The advantage of this alternativelies in particularly short reaction times required for completedepolymerization.

Particularly preferred depolymerizing agents are approximately 40%aqueous solutions of salts of dithiocarbamic acid, for example sodiumdimethyl dithiocarbamate. If a plasticizer of very low viscosity, forexample benzyl butyl phthalate, is used as the liquid medium, thesolutions/suspensions obtained after depolymerization have very lowviscosities. The percentage content of material to be depolymerized inthe mixture may thus be very high. 40 to 60% solutions/suspensions maybe processed without significant difficulties.

Although, in principle, the resulting solution/suspension of thedepolymerisate may also be incorporated in the so-called A component, itis preferred in accordance with the invention to incorporate thedepolymerisate mixture in the so-called B component, i.e. the curingcomponent. The A component is generally understood to be the componentwhich contains the generally liquid polysulfide and/or polymercaptanpolymer capable of undergoing the curing reaction. In addition to thepolysulfide and/or polymercaptan polymers just mentioned, this componentcontains plasticizers, generally phthalic acid esters, for examplebenzyl butyl phthalate; fillers, for example coated and/or uncoatedchalks (calcium carbonates, calcium magnesium carbonates), aluminiumsilicates, magnesium silicates, kaolin, heavy spar; thixotropicizingagents, for example Bentone (montmorillonite), pyrogenic silicas,fibrous thixotropicizing agents; pigments, for example titanium dioxide,carbon black and inorganic pigments; drying agents, for examplemolecular sieves, calcium oxide, barium oxide; the A component may alsocontain adhesion promoters, for example organofunctionaltrialkoxysilanes, and retarders, for example long-chain fatty acids(stearic acid and derivatives thereof), and also accelerators in theform of sulfur, magnesium acetate, thiurams, amines or guanidines.

In addition to the oxidizing agent acting as crosslinker, for examplelead dioxide, manganese dioxide, sodium perborate or organichydroperoxides, component B also contains plasticizers, fillers,retarders, pigments, sulfur, antiagers, optionally adhesion promotersbased on organofunctional trialkoxy or dialkoxy alkyl silanes andaccelerators, for example thiuram disulfides, guanidines,dithiocarbamates, and--according to the invention--between 2 and 80% byweight, preferably between 20 and 70% by weight and more preferablybetween 40 and 60% by weight of the depolymerisate.

It is new and completely surprising that the depolymerisates ofpolysulfides or polymercaptans can be used in the curing component,especially in such large quantities, without adversely affecting thecuring reaction or the stability of the compositions in storage.

The process according to the invention affords two major advantages overthe known recycling process, namely:

Firstly, there are no problems concerning stability in storage either inthe case of the A component or in the case of the B component.

It is now standard practice in the technology of two-componentpolysulfide and/or polymercaptan compositions to produce component A ina light color. This is because component B is dark in color through themanganese dioxide predominantly in use today, component B being adjustedto an anthracite color tone by pigmentation. By visually evaluating theuniformity of color of the mixed adhesive/sealant composition or coatingcomposition of components A and B, the user is able very easily to tellwhether the curing the composition has been fully mixed. If the materialto be recycled in incorporated in the A component, as proposed inDE-C-41 42 500, this component is darkened in color by thedepolymerisate, so that there are limits to the quantity in which the Acomponent can be taken up unless the user is prepared to relinquish thebasically indispensible advantage of simple visual control of the mixingefficiency for the A:B mixture.

The following Examples are intended to illustrate the invention withoutlimiting it in any way. In the Examples, the quantities in which theformulation constituents are used are parts by weight unless otherwiseindicated.

EXAMPLES

Preparation of the Depolymerisate Solution/Suspension

The following components were introduced with stirring into a heatablestirred tank reactor equipped with a propeller stirrer: benzyl butylphthalate, cured two-component adhesive/sealant based on polysulfide(Terostat 998 R, a product of Teroson GmbH), depolymerizing agent. Thesecomponents were then heated with stirring at 80° C. until a homogeneoussolution or suspension had formed, the polymer or its reaction productbeing completely dissolved in the plasticizer. The stability of thedepolymerisate in storage was followed by viscosity measurements for upto 4 months after its production. The results are set out in Table 1below.

                                      TABLE 1                                     __________________________________________________________________________    Production of the Recyclate                                                   Example    1    2   3   4   5   6   Comp. 1                                                                            Comp. 2                                                                            Comp. 3                         __________________________________________________________________________    Terostat 998R..sup.1.)                                                                   40   40  40  40  40  40  40   40   40                                Cured                                                                         Benzyl butyl phthalate 57 56 56 56 55 55 56 57 59                             N,N,N,N-Tetramethyl 1 -- -- -- 1 1 1 -- 1                                     guanidine                                                                     Mercaptosilane -- -- -- -- -- -- 3 2 --                                       Tetraethylene pentamine -- -- -- -- -- -- -- 1 --                             Tetrabenzyl thiuram 2 -- -- -- -- -- -- --                                    disulfide                                                                     Sodium dimethyl dithio- -- 4 -- -- -- -- -- -- --                             carbamate, 40% aqueous                                                        solution                                                                      Zinc dibutyl dithio- -- -- 4 -- 4 -- -- -- --                                 carbamate                                                                     Zinc dibenzyl dithio- -- -- -- 4 -- 4 -- -- --                                carbamate                                                                      100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00                                                            Solubility at 80°                                                     C. after 30 mins. 4 h 18 h                                                    6 h 10 h 10 h 15 mins. 40                                                     mins. 4 d                         Viscosity (Pa · s].sup.2.)                                           Immediately after 0.5 1.34 -- -- -- -- -- 0.6 Re-gels                         production                                                                    24 h after production -- 1.54 1.66 -- 0.77 0.96 -- 0.9                        3 d after production 0.6 1.51 1.60 2.78 -- -- -- Partly gels                  7 d after production 0.6 1.53 -- -- -- -- 3.3 --                              14 d after production 0.6 1.53 1.56 3.1 0.82 0.98  --                         3 w after production 0.7 -- 1.57 3.2 0.87 1.02 --                             4 w after production -- 1.66 -- -- -- -- --                                   5 w after production -- 1.73 1.59 3.2 0.86 1.22 --                            6 w after production 0.8 -- 1.70 3.4 0.97 1.11 6.74                           3 m after production 0.9 1.30 1.52 2.9 1.10 1.20 6.50                         4 m after production 0.6 1.35 1.00 2.2 0.60 1.00 6.1                        __________________________________________________________________________     Legend:                                                                       .sup.1.) Two component insulated glass adhesive/sealant based on              polysulfide, a product of Teroson GmbH                                        .sup.2.) Physica rotational viscosimeter, measuring system MC10, at D =       100 1/s and room temperature                                                  h = hour                                                                      d = day                                                                       w = week                                                                      m = month                                                                

Preparation of Curing Pastes

The curing pastes shown in Table 2 were prepared in a planetary mixerusing the depolymerisates and then further homogenized on a three-rollstand.

                  TABLE 2                                                         ______________________________________                                        Preparation of the Curing Pastes                                                  Example          7         8    9                                         ______________________________________                                        Recyclate of Example 1                                                                          43        50                                                  Recyclate of Example 2    50                                                  Manganese dioxide  23  23  23                                                 Benzyl butyl phthalate  3.0  4.5 7.0                                          Chalk, ground  6.0 -- --                                                      Heavy spar 10.7 10.0 6.54                                                     Filler/pigment mixture 20.7 14.0 10.54                                        Accelerator/retarder mixture.sup.1.) 10.3  8.5 9.46                           Viscosity [Pa.s].sup.2.) 358 172 139                                          Immediately after preparation                                                 24 d after preparation 393 154 --                                             7 d after preparation 413 191 165                                             2 w after preparation 340 -- 155                                              3 w after preparation -- 207 --                                               4 w after preparation 368 -- 159                                              5 w after preparation -- 144 --                                               6 w after preparation -- 185 --                                               7 w after preparation 348 -- --                                               8 w after preparation 369 141 157                                             3 m after preparation 270 160 130                                           ______________________________________                                         .sup.1.) Consisting of sulfur, tetramethyl thiuram disulfide,                 dithiocarbamate, amine accelerators, water and isostearic acid.               .sup.2.) Physica rotational viscosimeter, measuring system PP30, at D = 5     1/s and room temperature.                                                

Curing Tests:

The curing tests were carried out with the depolymerisate-containingcuring pastes according to the invention prepared as described aboveand, for comparison, with a commercial curing paste (Terostat 998 R,component B, a product of Teroson GmbH). A commercially availableadhesive/sealant (Terostat 998 R, component A, a product of TerosonGmbH) was used as component A. This adhesive/sealant is used for theproduction of laminated insulating glass. The test results are set outin Table 3 below.

As can be seen from Table 3, the properties (storage stability, pot lifecuring behavior) of the adhesive/sealant produced using thedepolymerisate-containing curing paste are no different from those ofadhesives/sealants produced using conventional curing pastes with noaddition of depolymerisate.

                                      TABLE 3                                     __________________________________________________________________________    Curing Behavior.sup.1.)                                                       Example     10                                                                              11 12 13 14 15 16                                                                              17 18 19 C4 C5 C6                              __________________________________________________________________________    Comp. B according to                                                                      7 7  7  7  8  8  8 9  9  9  B.sup.2.)                                                                        B.sup.2.)                                                                        B.sup.2.)                         Example                                                                       Tested after 4 d 4 w 6 w 8 w 14 d 4 w  24 h 14 d 4 w 24 h 14 d 4 w                                                         Pot life approx. 55 50 52                                                    50 55 58 52 57 48 44 50 50                                                    49                                (Hand-mixing [V], 23° C.)                                              Shore A after                                                                 1.5 h 22 24 22 18 17 30 21 30 35 40 27 26 27                                  2.0 h 36 38 25 31 31 43 32 40 43 42 37 37 40                                  2.5 h 44 44 34 37 37 43 37 40 43 43 42 42 44                                  3.0 h 40 46 37 41 40 46 42 47 43 43 42 43 44                                  4.0 h 42 48 45 44 48 46 44 50 46 44 44 43 44                                  5.0 h 45 50 47 46 48 48 46 50 48 44 45 45 45                                  24 h 45 50 47 47 48 48 47 50 48 45 46 46 46                                   3 d 46 50 48  50 48  43 48  46 46 47                                        __________________________________________________________________________     .sup.1.) A commercial twocomponent polysulfide adhesive/sealant (Terostat     998 R, a product of Teroson GmbH) was used as component A; mixing ratio       A:B = 10:1 (by volume)                                                        .sup.2.) Comparison tests with a commercially available component B           (Terostat 998 R, a product of Teroson GmbH)                              

                  TABLE 4                                                         ______________________________________                                        Adhesion Test                                                                   Example       11      11   14    14   17    17                                Adhesion after 24 h 3 d 24 h 3 d 24 h 3 d                                   ______________________________________                                        Glass       CF      CF     CF    CF   CF    CF                                  Aluminium CF CF CF CF CF CF                                                   Galvanized steel CF CF C/A CF CF CF                                           plate   1:1                                                                 ______________________________________                                    

In Examples 11 to 17 (Table 4), components A and B were mixed in a ratioby weight of 10:1. For the adhesion test, strands were applied to thesubstrates to be tested. They were peeled off by hand and the fracturepattern was evaluated. CF stands for cohesive failure while C/A standsfor a mixed fracture pattern with cohesive components and partial lossof adhesion (ratio about 1:1).

In Comparison Examples 1 and 2, a recyclate was produced in accordancewith EP-B-188 833. Comparison Example 3 was carried out on the basis ofstandard expert knowledge. Although, in all three Comparison Examples,the cured adhesive/sealant is degraded more or less quickly, therecyclate regels after only a relatively short time, presumably underthe effect of atmospheric oxygen.

Unstable recyclates such as these are unsuitable for reuse. By contrast,the recyclates of Examples 1 to 6 according to the invention give pasteswhich remain stable in viscosity over a long period. By virtue of theshort reaction time required, the procedures of Examples 1 and 2 areparticularly advantageous.

As can be seen from Table 2, not only the recyclate pastes, but also thecuring pastes produced from them remain stable in storage (stable inviscosity) over a long period.

Table 3 shows that the curing pastes produced in accordance with theinvention--in relation to component A of a commercial polysulfideadhesive/sealant--are entirely equivalent in their curing behavior to aconventional component B curing paste according to the prior art.

It can be seen from Table 4 that the favorable adhesion behavior of thetwo-component adhesive/sealant produced using the recyclate-containingcuring paste according to the invention on all standard substratesremains unaffected.

What is claimed is:
 1. A process for recycling cured or partly curedpolysulfide and polymercaptan polymer compositions, comprising the stepsof:depolymerizing a polymer selected from the group consisting ofpolysulfides, polymercaptans and mixtures thereof with a depolymerizingagent to form a depolymerisate; and incorporating said depolymerisate inthe curing component of a composition selected from the group consistingof two-component polysulfides, polymercaptans and mixtures thereof. 2.The process as claimed in claim 1, wherein said depolymerizing agent isa vulcanization accelerator.
 3. The process as claimed in claim 2,wherein said vulcanization accelerator is selected from the group ofthiazole accelerators, thiurams, dithiocarbamates, dithiocarbamylsulfenamides, xanthogenates, sulfur-containing triazine accelerators,thiourea derivatives and mixtures thereof.
 4. The process as claimed inclaim 2, wherein said vulcanization accelerator is a basic sulfurcompound.
 5. The process as claimed in claim 1, wherein saiddepolymerizing agent is an aqueous solution of the salt of avulcanization accelerator.
 6. The process as claimed in claim 1, whereinthe depolymerization step is carried out in a plasticizer.
 7. Theprocess as claimed in claim 1, wherein the depolymerization step iscarried out at temperatures of about 0° C. to about 100° C. 8.Two-component or multi-component compositions based on polysulfides andpolymercaptans, comprising a curing component comprising about 2 toabout 80% by weight, of a depolymerisate produced by the process claimedin claim
 1. 9. Two-component or multi-component compositions based onpolysulfides and polymercaptans, comprising a curing componentcomprising about 20 to about 70% by weight of a depolymerisate producedby the process claimed in claim
 1. 10. Two-component or multi-componentcompositions based on polysulfides and polymercaptans, comprising acuring component comprising about 40 to about 60% by weight of adepolymerisate produced by the process claimed in claim
 1. 11.Compositions as claimed in claim 8, wherein the curing component furthercomprises an oxidizing agent selected from the group consisting of leaddioxide, manganese dioxide, compounds of hexavalent chromium andmixtures thereof.